Anisotropic particles: synthesis and characterization of responsive rod-like colloids

Abstract

This thesis describes the development of model functional rod-like particles, based on silica microrods or fd-virus particles, for further study of their self-assembly behaviour in colloidal phases. Silica rods were first functionalised by grafting a pH- and temperature-responsive polymer, poly(2-(dimethylamino)ethyl methacrylate) (PDMA) onto their surface, using both “grafting from” and “grafting to” techniques in combination with atom transfer radical polymerisation (ATRP). The polymer content of the “grafted from” rods was found to decrease after dispersion for a few days in water, which is detrimental for their further characterisation and use. This phenomenon was attributed to the degrafting of the polymer chains, due to the hydrolysis of labile surface bonds, which was mechanically activated by the tension of the chains. The degrafting was delayed by first grafting a hydrophobic layer on the particles, that acts as a barrier for the penetration of water molecules. Next, the synthesis of hollow polymer rods from amphiphilic block copolymer brushes grafted onto the surface of the silica rods is discussed. Robust polymer microrods were obtained following the etching of the silica core, even in the absence of chemical cross-links within the polymer layer. In the next part of this work, a TiO 2 layer was coated onto the surface of the silica rods, by a surfactant induced precipitation process. A uniform coating on the surface of the rods, without any side nucleation, was realized, yielding a TiO 2 layer with tunable thickness. Finally, the silica cores were etched to obtain hollow amorphous TiO 2 rods, which caved in after drying, or robust crystalline TiO 2 tubes. In the last part of this work, end-functional responsive polymers were synthesised to be “grafted to” fd-virus particles in aqueous media, utilising the amino groups present on the fd-virus surface. Fluorescent and non-fluorescent pH- and temperature-responsive PDMA, was synthesised by ATRP. In addition, well-defined end-functional PNIPAM polymers were synthesised by reversible addition-fractionation chain-transfer polymerisation (RAFT), and grafted onto fd-virus particles. Finally, PEG-b-PNIPAM copolymers were also synthesised by RAFT to be “grafted to” fd-virus particles and obtain anisotropic colloids whose volume can be tuned without inducing any attractive interparticle interactions.

Η παρούσα διδακτορική διατριβή περιγράφει την ανάπτυξη καινοτόμων λειτουργικών ραβδόμορφων σωματιδίων πυριτίας, οξειδίου του τιτανίου και πολυμερούς καθώς και του ιού fd με στόχο την περαιτέρω μελέτη της αυτό-οργάνωσης τους σε κολλοειδείς υγροκρυσταλλικές φάσεις.